The present invention generally relates to a telephone controller for controlling a telephone and coupling the telephone to a telephone line. More particularly, the present invention relates to a circuit which is preferably fabricated in a single integrated circuit and provides the resources necessary to construct a telephone product that functions as a telephone, a digital answering machine, a speakerphone or ADSI controller. By integrating all of these resources into a single integrated circuit, and by providing these functions using a single digital signal processor, the present invention achieves unique economies not heretofore realizable.
Since telephone products such as telephones, answering machines and speakerphones are consumer products, they are particularly sensitive to issues of cost. Any telephone product which can be manufactured less expensively than other competing products, while providing the same or additional features, enjoys a significant commercial advantage over the competing products. Accordingly, in the design and development of components for telephone products, it is desirable to minimize the cost of such components, as well as the costs associated with manufacturing and interconnecting such components.
It is also desirable, in the design of components for telephone products, to provide as many functions and features as is economically feasible. Unique features provide an additional economic advantage over competing products. Moreover, the presence of multiple features in a single telephone product or in a component for a telephone product allows a manufacturer to provide a product line having a range of operational features simply by activating or deactivating these features. In this manner, a manufacturer can present a broad line of products while minimizing manufacturing costs. High end and low end products can be manufactured using identical components, with additional features activated in the high end products during manufacturing.
It is commercially desirable to combine into a single consumer telephone product most of the commonly available telephone features. Such a telephone product provides a telephone, a digital answering machine, and a speakerphone with ADSI capability. A telephone comprises, at a minimum, a handset including a microphone and an earpiece and a keypad for dialing. An electronic telephone may also need to generate a dial tone, busy tones and ringing tones. Accordingly, a digital signal processing means is needed in conjunction with a telephone for generating audible outputs including a dial tone, busy tones and ringing tones.
Analog Display Services Interface, or ADSI, is a standardized protocol for interfacing to a display-based telephone. The display-based phone is generally a plain old telephone set (POTS) with a character display, such as a liquid crystal display. The protocol supports a variable display size, up to a maximum of 33 lines by 40 characters. The phone also contains various "soft keys" which are programmable and analogous to the function keys on a personal computer keyboard. Under the ADSI protocol, data is transmitted to the phone, using the same line as voice transmissions. The data are encoded, for example, using frequency shift keying (FSK). The encoded data are received and decoded to form digital data. A portion of the data may be displayed on the display, while another portion of the data may control operation of the telephone, including programming the soft keys. Voice data may also be transmitted to provide audible prompting of the user. Responses from the telephone, including data from the programmable soft keys, are encoded using dual tone, multiple frequency (DTMF) codes, and conveyed over the same telephone line. Accordingly, a digital signal processor means is needed in conjunction with an ADSI controller to function as a modem for receiving and decoding the FSK data to digital data and for encoding digital data as DTMF tones.
A digital answering machine provides the same functionality as traditional tape answering machines but stores messages in solid state memory, rather than on magnetic tape. The elimination of mechanical parts needed for transporting the tape increases reliability over tape answering machines. Also, the integrated circuits necessary for implementing a digital answering machine require far less physical space than a tape answering machine. The digital answering machine stores one or more outgoing messages, and one or more incoming messages. The digital answering machine may also perform voice synthesis from data stored in memory. A synthesized voice message may be provided as a time and date stamp for recorded messages. To reduce physical memory requirements, voice data are preferably compressed for storage and decompressed for playback. The digital answering machine may be controllable by keypad entries received from the telephone keypad or by DTMF tones received from remote locations over the telephone lines. Accordingly, a digital signal processing means is needed in conjunction with a digital answering machine for converting an analog audible input to digital data and digital data to an analog audible output, converting DTMF codes to digital data, and performing the compression and decompression algorithms.
A speakerphone allows hands-free operation of a telephone. The speakerphone includes a speaker for converting electrical signals representative of speech to audible sound, and a microphone for converting an audible input such as speech to electrical signals. A control circuit monitors electrical signals supplied to the speaker and received from the microphone in order to independently activate either the speaker or the microphone. A speakerphone switch may be provided to activate the speakerphone microphone and speaker while deactivating the telephone handset microphone and earpiece. When used in combination with a digital answering machine, the speakerphone microphone may be employed for recording outgoing messages and the speakerphone speaker may be employed for playing back recorded outgoing messages or incoming messages. Accordingly, a digital signal processing means is needed for converting analog voice signals to digital data, comprising digital data, decompressing compressed digital data and converting digital data to voice signals.
Implementing a telephone controller requires an analog interface for coupling the telephone controller to the telephone line. The telephone line conveys telephone signals over two wires, commonly known as tip and ring. Telephone signals, including ringing signals, are standardized. The analog interface must receive analog input signals from tip and ring, supply analog output signals to tip and ring, receive audible input signals from a handset microphone, provide audible output signals to a handset earpiece, and provide sidetone. A sidetone path provides a portion of the outgoing voice signal to the handset earpiece to provide a more comfortable interface for the user.
As is apparent, considerable hardware is required when combining the structure necessary to perform the functions of a telephone, digital answering machine, speakerphone and ADSI controller. In particular, each of these devices requires a digital signal processor. Moreover, the functions performed by the different signal processors may need to be performed simultaneously, such as DTMF detection during analog-to-digital conversion and data compression. A control means such as a microcontroller is further needed for coordinating the different functions of the combined telephone product.
Moreover, for robustness, such a combined telephone product should provide more than one operating mode. Preferably, the product is operable from AC power supplied through a line cord. In the event of a power outage, the product should continue to provide telephone functions, powered from the telephone line. Since a digital signal processor and a microcontroller operate in response to a program of instructions, such a combined telephone product should include an in-circuit emulation mode for developing the program of instructions.
One known telephone product provides telephone and digital answering machine functions in five separate integrated circuits. One chip includes a voice processor; a second chip provides a codec, including analog-to-digital and digital-to-analog conversion; a third chip provides a data access arrangement for coupling to a telephone line; a fourth chip provides a microcontroller for the voice processor; and a fifth chip provides a microcontroller for the data access arrangement and the keyboard. This product requires at least two digital signal processors, one for the voice processor chip and one for digital-to-analog and analog-to-digital conversion and filtering.
Such a multiple chip design is expensive to implement in a consumer telephone product. Five different integrated circuits require substantial area or "real estate" on a printed circuit board. Them any interconnections between the devices add to manufacturing cost and time and reduce product reliability. A design which requires two digital signal processors requires development of two independent programs of instructions, adding to development time and cost. Moreover, the use of two digital signal processors is duplicative and inefficient, wasting energy and real estate.
Accordingly, there is a need in the art for a single integrated circuit device which combines the functions of a telephone controller, a digital answering machine controller, a speakerphone controller and ADSI. The present invention provides such a device and thereby provides unique cost and performance advantages not realizable by prior art devices. Integration within a single integrated circuit allows use of a single digital signal processor to control all of the functions of the telephone controller. The single chip integrates both digital and analog functions of the controller, thus reducing noise on analog signal paths and subsequent inaccuracies in digital signals. Integration into a single integrated circuit requires fewer parts to implement a telephone product which combines all these features, and therefore fewer interconnections. This reduces manufacturing costs and improves reliability. Moreover, use of a single chip reduces power consumption, since high-power output circuits needed to drive signals between discrete integrated circuits are not necessary. Also, use of a single integrated circuit allows on-chip control of functions such as signal attenuation and filtering, ring detection, and off-hook detection, as well as different modes of operation, such as active mode, low power shutdown mode, and in-circuit emulation mode.